This invention pertains to the phase separation of hydrogenated hydrocarbon liquids at elevated temperature and pressure conditions, and particularly to a phase separation flow configuration for minimizing undesired coke formation in a hot gas-liquid separation step or device.
In catalytic hydrogenation processes for heavy petroleum oil and coal feedstreams, such as for the H-Oil.RTM. and H-Coal.RTM. processes, a continuing problem has been deposits of carbon in the hot phase separator located immediately downstream from the catalytic reaction zone, wherein a vapor stream is separated from the reactor effluent slurry. Because of the high temperature conditions and with a deficiency of hydrogen, carbonaceous deposits usually form on the interior wall of the hot separator apparently at the interface between the vapor and liquid phases, particularly if this interface is moving as, for example, when the hot slurry is splashing on the separator inner wall.
This solids deposition problem in the hot phase separator following a hydrogenation step is difficult to avoid, because the reactor effluent slurry contains a gaseous portion, and the purpose of the phase separator is to remove the gas from the liquid. As a result, there is extensive bubbling and frothing within the separator, and it is essential to provide a considerable liquid surface from which the gas can evolve effectively. At the same time, it is desirable to minimize the solid or wall surface exposed to the froth and minimize the interface between the solid walls and the liquid by promoting a stable flow.
Numerous previous attempts to solve this coking problem in the hot separator have been made. For example, in the hydroconversion of tar sand bitumen feedstocks to produce lower-boiling liquid products, quenching the hot reactor effluent stream in the phase separator to quickly cool the oil and avoid coking has been used, as described by U.S. Pat. Nos. 3,841,981, 3,842,122 and 3,844,937. Also, in the hydrogenation of coal slurry feedstocks to produce lower-boiling product liquids and gas, a hot separator shaped to control settling velocity for liquid and contained solids has been used, as described in U.S. Pat. No. 4,151,073 to Comolli. However, troublesome deposits of coke on the hot separator vessel inner walls still sometimes occur when processing hot hydrocabon liquids, so that further improvements are desirable.